1. Field of Invention
This nonprovisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No(s). 92129664 filed in TAIWAN, R.O.C. on Oct. 24, 2003, which is(are) herein incorporated by reference.
The invention relates to an edge emitting laser and, in particular, to a edge emitting laser with circular beam that uses a low-carrier-mobility material.
2. Related Art
Semiconductor lasers have the features of compact sizes, long lifetime, good vibration tolerance, being highly directional, and large output power. They are ideal for the light sources of long-distance, large-capacity communications and high-density recording media. Currently, most of their applications are in optical communications and storage industries. Therefore, the semiconductor lasers have a brighter future.
According to their structures and light-emitting position, the semiconductor lasers are divided into surface-emitting lasers and edge emitting lasers. The cavity of the edge emitting laser is parallel to the epitaxy layer. The reflecting surface is formed by coating a reflecting film on the cutting surface of a crystal. It is perpendicular to the epitaxy layer. Light reflects between two side mirrors (i.e. inside the cavity) and sends out a laser beam through a side surface. Since the thickness of ridge waveguide is much larger than active region, the light intensity distribution is a vertical ellipse. Thus, it has a very bad coupling efficiency, limiting its applications.
Consequently, we want to use a specially designed edge emitting laser structure to improve the roundness of the laser beam. A vertical groove through the light-emitting layer is formed using an etching means, thereby generating a horizontal light diffractive index difference. Total reflection occurs between the light-emitting layer and the medium with a lower reflective index. Horizontal light is thus trapped inside the light-emitting layer. This increases the spreading angle of the laser beam in the horizontal direction, achieving the goal of a circular beam. The light-emitting layer material used in conventional edge emitting laser with circular beams has series carrier surface recombining effects at the etching interface, resulting in a low light-emitting efficiency. Therefore, after etching though the light-emitting layer the groove thus formed has to be grown with the epitaxy of other semiconductor materials, forming the so-called buried ridge waveguide. However, such a structure does not only involve complicated manufacturing processes but also has a higher cost. The reflective index difference between the semiconductor material and the light-emitting layer material is smaller. As a result, the roundness of the circular beam is not perfect.